Pass argument into hashtable_new
    
    @8915d8d87 and @4471b7350 modified "usetxn" parameter in
    "hashtable_new" scope (was a global variable before).
    But the callers of this function don't pass argument into.
    Thus, "usetxn" acts as an uninitialized auto variable.
    
    Fixes: https://pagure.io/389-ds-base/issue/50057